1. Technical Field
The disclosed technology relates to radio frequency (RF) receiver architectures, waveforms, and algorithms for signal processing. More specifically, the disclosed technology relates to RF receiver architectures and algorithms for signal processing as applied to semi-active missile guidance.
2. Brief Description of the Related Art
An incoming missile or other threat can be thwarted with an interceptor missile (or interceptor), which is a high-speed defensive missile designed to take out the incoming (target) missile before the target missile can reach its intended destination. An important class of interceptor uses RF radar signals to provide the guidance information needed to intercept the moving target. Semi-Active radar seekers receive the target radar return from RF signals transmitted by an illumination radar residing at some fixed location. Radar seekers in the interceptors typically employ multiple RF channels to receive and process the radar returns from the target. The interceptor seeker derives an intercept guidance solution from the range, range rate, direction angle, and angle rate from measurements generated by the radar return.
For example, a current active protection system (APS) long-range guided interceptor uses a multi-channel (four-channel) radio frequency (RF) seeker for intercept. Such systems typically require four antenna elements to estimate the target bearing by measuring the angle of arrival of the target RF return. Interferometer or monopulse processing is used to determine the angle of arrival by comparing the relative RF phase difference of the signals received in each of the four channels.
A standard monopulse seeker typically uses a conventional pulsed radar waveform, with multiple receive elements and multiple RF/intermediate frequency (IF) receiver channels. Accurate angle of arrival measurements demand that these receive channels must be matched in amplitude and phase. In addition, the phase of arrival can be distorted by the presence of aerodynamic radomes used in high-speed interceptors. These distortions must be measured and corrected using calibration and compensation techniques. Thus, to meet accuracy and timing requirements of interceptor missile seekers, phase balance is required, amplitude balance is required, and fast, accurate calibration is required. These requirements can be difficult to achieve in a small low-cost, expendable, seeker design.